Plant propagation methods: a refresher

By Vina Medenilla

Plant propagation is a process of growing new plants from existing ones. It helps to increase the number of plants, whether replicas of parent plants or new varieties. Aside from it being an easy process, plant propagation also enables people to spend less in multiplying plants at home.

There are two methods of plant propagation: sexual and asexual. 

Sexual propagation is a way of growing plants through the use of seeds. Two types of seeds are orthodox and recalcitrant. One sexual propagation technique is through hydroponic culture. 

• Orthodox, also known as durable seeds – These seeds are tolerant of drought and low temperatures. Examples include cereals and beans. 

In a study called Seed Moisture: Recalcitrant vs. Orthodox Seeds, orthodox seeds require low seed moisture content for long-term storage, while recalcitrant seeds need to retain high moisture levels and can only be stored for one to two weeks, according to the website agroforestry.org. 

Danilo R. Piñera, Ph.D., a retired professor and manager under the Crop Science Department of Isabela State University, said that orthodox seeds are the type of seeds that need further drying through sun exposure or else its embryo will die.

An example offered by Piñera is rice. If one desires to keep the seed for about six months to a year, its moisture content must be less than 14%. Usually, the lower the moisture content, the higher the abscisic acid in the orthodox seed. Abscisic acid is the acid that restricts the entry of water into the seeds. It makes it waterproof and unviable to grow. If this is the case, to break its dormancy before planting, it is important to keep the seed exposed to direct sunlight for one to two hours between 12 to two o’clock in the afternoon to ensure its growth. After drying, sow it immediately. If it is not dried before sowing, it will remain dormant and the water will not be absorbed. Hence, it will not grow.

• Recalcitrant or horticultural seed – This refers to seeds that need to be sowed right away to ensure that its embryo stays alive. Unlike orthodox seeds, recalcitrant seeds cannot withstand low moisture content levels and freezing temperatures. Recalcitrant seeds need to hold a high moisture content to keep its embryo alive. Examples are rambutan and jackfruit seeds. If the moisture content of this seed is not maintained, it lowers the percentage of germination and plant growth. 

Asexual or vegetative propagation is a method of growing plants without the use of seeds. This is done by taking vegetative parts of the parent plant such as stems, roots or leaves and allowing it to regenerate onto another plant. This allows one to grow an identical plant, or a clone of the parent plant. So if one plant has notable characteristics, reproducing the same plant is possible through this method. Many plants can be reproduced through just one parent plant, and these clones can also grow faster than those grown from the seed. But if the parent plant has a disease, there is a high risk of transferring said disease to the new plant. Grafting and marcotting are examples of this, as well as water bonsai.

Pot and root system

In propagating plants, having the right pot size is important for the plant’s growth and root system to flourish. If the plant grows 10 meters aboveground, then it must have a rootstock at least 10 meters below as well, Piñera said. 

Undersized pots mean that the plant’s root system is limited because it will not reach deep enough. Small pots with minimal soil may have a strong possibility of  dehydrating the plant growing in it if not maintained well. Likewise, having an oversized pot for the plant also involves a high risk of it watering too much or too little. This can lead to root decay and other root diseases. Either way, it can both hinder and slow down plant growth due to the lack of nutrients. Therefore, choosing an appropriate pot does not just help the proper growth of the propagated plant below the ground but also the growth of the roots underneath.

Insights from Danilo R. Piñera, Ph.D., during the Nursery Management and Plant Propagation seminar last February 21, 2020, at Agricultural Training Institute (ATI) Compound in Quezon City.